Recently radars are being increasingly used for the purpose of detecting and finding the range and speed of moving objects by transmitting a beam of radio frequency or microwave energy in the general direction of the object. Radar detectors have been accordingly used for the purpose of checking whether or not a prescribed radar is actually radiating a beam of radio-frequency energy.
There are a variety of types of radar detectors. All of these radar detectors are liable to be adversely affected by noise signals in the form of pulses. False detections by a radar detector are often caused by signals of radio-frequency energy transmitted by other nearby radar detectors which run on the same signal-receiving principle. Also, there is a relatively high probability of false discrimination being caused by interpreting of a microwave beam transmitted by one of the prescribed radars for another microwave beam transmitted by a radar other than a prescribed one.
In an attempt to eliminate such false discrimination a variety of anti-malfunction circuits have been proposed. Most of these anti-malfunction circuits use a digital type discriminator for discriminating the prescribed beam of radio frequency energy from among others. The digital type discriminator, however, is complicated in structure, and expensive.
Also, disadvantageously a digital type discriminator does not work when the frequency of an interference signal fluctuates with a period which is an integer multiple of the local frequency sweeping period. Radar detectors equipped with a digital type discriminator tend to have reduced sensitivity in detecting signals of very small energy. For these reasons conventional radar detectors are not satisfactory.